Radar transmitter circuitry and techniques

Abstract

A radar transmitter includes a digital ramp generator circuit for generating a VCO control signal. The ramp generator includes a digital signal processor and a digital-to-analog converter. In one embodiment, the VCO output signal is up-converted to provide the transmit signal and in another embodiment, the VCO operates over the transmit frequency. Also described is a VCO comprising a DR and a phase shifter. A temperature compensation feature includes detecting the transmit frequency and comparing the DSP output generating the detected frequency to a DSP output stored in association with the detected frequency. Also described is a technique for compensating for non-linear VCO operation in which the DSP output words are adjusted to provide a waveform complementary in shape to the non-linear VCO characteristic. Susceptibility of the radar to interference is reduced by randomly varying at least one parameter of the ramp signal, such as offset interval or voltage range, in at least one ramp signal cycle.

What is claimed is:  
     
       1. A radar transmitter comprising: 
       a DSP having an output terminal at which a digital output word is provided;  
       a D/A converter having an input terminal coupled to the output terminal of the DSP and an output terminal at which an analog ramp signal is provided; and  
       a VCO having an input terminal responsive to the analog ramp signal and an output terminal at which a frequency modulated signal is provided.  
     
     
       2. The radar transmitter of  claim 1  further comprising a smoothing circuit having an input terminal coupled to the output terminal of the D/A converter and an output terminal coupled to the input terminal of the VCO. 
     
     
       3. The radar transmitter of  claim 1  further comprising an up-converter having an input terminal coupled to the output terminal of the VCO and an output terminal at which a transmit signal is provided. 
     
     
       4. The radar transmitter of  claim 3  wherein said up-converter comprises a DRO. 
     
     
       5. The radar transmitter of  claim 1  wherein said VCO comprises: 
       an amplifier having an input terminal to which a terminator is coupled and an output terminal;  
       a phase shifter having an input terminal coupled to the output terminal of the amplifier, an output terminal at which a frequency modulated signal is provided, and a control terminal; and  
       a DR positioned to couple energy from the output terminal of the phase shifter to the input terminal of the amplifier.  
     
     
       6. The radar transmitter of  claim 1  further comprising: 
       a memory in which is stored a look-up table containing a plurality of DSP output words in association with an expected transmit frequency;  
       a frequency detection circuit for detecting the frequency of a transmit signal generated by the frequency modulated signal; and  
       a comparator for comparing a DSP output word from which the detected frequency is generated with a DSP output word stored in the look-up table in association with the detected frequency to provide an error value.  
     
     
       7. The radar transmitter of  claim 6  wherein said frequency detection circuit comprises a DR having a fundamental frequency substantially equal to the detected frequency. 
     
     
       8. The radar transmitter of  claim 6  further comprising an offset generator for adjusting the output word of the DSP in response to the error value. 
     
     
       9. The radar transmitter of  claim 1  further comprising a random number generator for varying at least one parameter of the analog ramp signal. 
     
     
       10. The radar transmitter of  claim 9  wherein the at least one parameter is selected from an offset interval and a voltage range. 
     
     
       11. The radar transmitter of  claim 1  wherein said transmitter comprises a side object detection module of a near object detection system. 
     
     
       12. A method for compensating for temperature induced variations in a radar system comprising the steps of: 
       generating, from a predetermined sequence of digital words, a transmit signal having a frequency associated with a respective word of the predetermined sequence of digital words;  
       storing each word of the predetermined sequence of digital words in association with an expected transmit signal frequency;  
       detecting the actual frequency of the transmit signal;  
       comparing the digital word from which the actual frequency is generated to a digital word stored in association with the actual frequency to provide an error value; and  
       adjusting each word of the predetermined sequence of digital words in response to the error value.  
     
     
       13. The method of  claim 12  wherein said adjusting step includes offsetting each word of the predetermined sequence of digital words by the error value. 
     
     
       14. The method of  claim 12  wherein said detecting step includes detecting the actual frequency of the transmit signal with a DR having a fundamental frequency substantially equal to the actual frequency. 
     
     
       15. A method for reducing interference between radar systems comprising the steps of: 
       generating a ramp signal for controlling to a VCO; and  
       randomly varying at least one parameter of said ramp signal.  
     
     
       16. The method of  claim 15  wherein said ramp signal comprises a plurality of cycles, each comprising an offset portion, a ramp portion, and a CW portion and wherein said at least one parameter is randomly varied in at least one of said plurality of cycles. 
     
     
       17. The method of  claim 16  wherein the at least one parameter is selected from the duration of said offset portion and a voltage range of said ramp portion. 
     
     
       18. A method for compensating for non-linear operation of a VCO in a radar transmitter, comprising the steps of: 
       measuring the output frequency of the VCO in response to a plurality of input voltage levels to the VCO to provide a characteristic curve of the VCO;  
       determining a complementary waveform with respect to the characteristic curve; and  
       providing a sequence of output words of a DSP operable to generate a transmit signal for generating the complementary waveform.